Ok, don't Deny Write to the group. That's the first thing. A Deny will trump Everything else. If you Deny a group anything, then any member in that group can't is, obviously, denied from doing that function. Nothing you could then do would let any member of that group have the ability.
So, here's what you do. Just don't Enable the write ability to the original group. Don't click the Deny box, and don't click the Enable box for write. Leave both boxes blank for the group.
Then make a new Global group, and put the 5 users in it. Users can be in more that 1 Global groups!
Then give this new Global group the write ability to this folder.